Efficient energy storage is one of the most important challenges on the way to building an economy that is less dependent on fossil fuel resources. Current implementations of electrochemical energy storage devices, such as batteries, supercapacitors, and fuel cells, use a variety of electroactive species. Common examples include lead-acid (Pb and H2SO4), nickel-cadmium (NiOOH and Cd), nickel-zinc (NiOOH and Zn), lithium-ion (various Li compounds), and nickel-metal hydride (NiOOH and various intermetallic compounds).
Metal-air batteries, and more specifically lithium-air batteries, are thought of as key enablers of electric vehicles, largely because of their very high energy densities. However, currently, metal-air batteries are unable to meet the conditions required for practical vehicle applications. Existing lithium-air battery designs are plagued with lithium oxide (Li2O) and lithium peroxide (Li2O2) clogging the pores of the air-electrode, thus limiting discharging capacity. Additionally, moisture or nitrogen from the air may cause hazardous reactions. Furthermore, lithium-air batteries suffer from unproven recharge capability, limited lithium resources, and environmentally hazardous construction.
The electrolytes utilized in electrochemical energy storage devices are also significant to device performance. Typical electrolytic solutions consist of ion-forming solutes dissolved in water or organic solvents. Many of these electrolytes are toxic or flammable, further adding to the hazards of device construction, use, and disposal. U.S. Pat. No. 7,579,117 attempts to address these problems by suggesting the use of supercritical carbon dioxide (CO2) as a solvent. Although successfully applying supercritical CO2 as a solvent, U.S. Pat. No. 7,579,117 requires another electroactive species, stressing that the supercritical CO2 is virtually inert, and does not react with other elements in the electrochemical cell.
These implementations suffer from a variety of disadvantages, including low energy density; harmful environmental impact in construction, use, and disposal; inefficiency in charging or discharging; and safety hazards during use, including risk of fire or explosion if misused or punctured.